The essays in this volume address three fundamental questions in the philosophy of science: What is required for some fact to be evidence for a scientific hypothesis? What does it mean to say that a scientist or a theory explains a phenomenon? Should scientific theories that postulate "unobservable " entities such as electrons be construed realistically as aiming to correctly describe a world underlying what is directly observable, or should such theories be understood as aiming to correctly describe only the observable world? Distinguished philosopher of science Peter Achinstein provides answers to each of these questions in essays written over a period of more than 40 years. The present volume brings together his important previously published essays, allowing the reader to confront some of the most basic and challenging issues in the philosophy of science, and to consider Achinstein's many influential contributions to the solution of these issues. He presents a theory of evidence that relates this concept to probability and explanation; a theory of explanation that relates this concept to an explaining act as well as to the different ways in which explanations are to be evaluated; and an empirical defense of scientific realism that invokes both the concept of evidence and that of explanation.

What is meant by scientific evidence, and how can a definition of this concept be applied in the sciences to determine whether observed facts constitute evidence that a given theory is true?
In this book, Peter Achinstein proposes and defends several objective concepts of evidence. He then explores the question of whether a scientific method, such as that represented in the four "Rules for the Study of Natural Philosophy" that Isaac Newton invoked in proving his law of gravity, can be employed in demonstrating how the proposed definitions of evidence are to be applied to real scientific cases. In answering this question, he offers a new interpretation of Newton's controversial rules. Contrary to what many methodologists assume, whether the rules, so interpreted, can be used to determine whether observed phenomena provide evidence for a theory is an empirical question, not an a priori one. Finally, in order to deal with numerous cases in which evidence is insufficient to establish a theory, or where no theory is even available, Achinstein describes and defends three scientific methods proposed by the 19th century theoretical physicist James Clerk Maxwell, in the course of developing his electrical and molecular theories.

Offering a new approach to scientific explanation, this book focuses initially on the explaining act itself. From that act, a "product" emerges: an explanation. To understand what that product is, as well as how it can be evaluated in the sciences, reference must be made to the concept of the explaining act. Following an account of the explaining act, its product, and the evaluation of explanations, the theory is brought to bear on these issues: Why have the standard models of scientific explanation been unsuccessful, and can there be a model of the type sought? What is causal explanation, and must explanation in the sciences be causal? What is a functional explanation? The "illocutionary" theory of explanation developed at the outset is used in discussing these issues, and contrasting philosophical viewpoints are assessed.

Newton urged scientists never to speculate, only to prove by establishing experimental facts. By contrast, Einstein urged scientists to speculate freely, since only daring speculations, not experimental facts, can advance science. Who, if either, is right? Is speculation a legitimate part of science, even in the absence of testing? If so, can speculations be evaluated without testing? How? To answer these questions it must first be determined what counts as a speculation, a task not usually investigated by those who express strong views about speculation. In Speculation, Peter Achinstein develops the basic idea that speculating involves introducing assumptions, under certain "theorizing" conditions, without knowing that there is evidence for those assumptions. This idea is made precise by utilizing a concept of "evidence" Achinstein has introduced in previous writings and also explains here. With this concept, Achinstein defends a view according to which, by contrast with Newton, speculations are crucial in science, and by contrast with Einstein, they are subject to constraints. The latter include pragmatic ones, reflecting the particular aims of the scientist in speculating, and epistemic ones that are subject to a different standard then "evidence sufficient for belief." This viewpoint is illustrated and evaluated by critically examining historical and contemporary speculations in fundamental physics as well as more general speculations within or about science, including these: nature is simple, and simplicity is a sign of truth (Newton, Einstein); a theory can only be tested "holistically" (Duhem and Quine); and there is, and must be, a "Theory of Everything" (string theorists and reductionists).

Achinstein explores the question of how something comes to be considered as evidence for a theory, claims that most surrent theories are too weak to give scientists a good reason to believe in the value of evidence, and ultimately develops his own theory of evidence.

This volume brings together six published and two new essays by the noted philosopher of science, Peter Achinstein. It represents the culmination of his examination of methodological issues that arise in nineteenth-century physics. He focuses on the philosophical problem of how, if at all, it is possible to confirm scientific hypotheses that postulate `unobservables' such as light waves, molecules, and electrons. This question is one that not only was of great interest to nineteenth-century physicists and methodologists, but continues to occupy philosophers of science up to the present day. The essays in this volume deal with this vexing problem as it arose in actual scientific practice in three nineteenth-century episodes: the debate between particle and wave theorists of light, Maxwell's kinetic theory of gases, and J.J. Thomson's discovery of the electron. Achinstein shows that the most important issue raised by these three cases concerns the legitimacy of introducing hypotheses that invoke "unobservables". If science is to be empirical, can such hypotheses be employed? How, if at all, is it possible to confirm them? Achinstein here assesses the philosophical validity of nineteenth-century and modern answers to these questions and presents and defends his own solutions.

Is there a universal set of rules for discovering and testing scientific hypotheses? Since the birth of modern science, philosophers, scientists, and other thinkers have wrestled with this fundamental question of scientific practice. Efforts to devise rigorous methods for obtaining scientific knowledge include the twenty-one rules Descartes proposed in his "Rules for the Direction of the Mind" and the four rules of reasoning that begin the third book of Newton's "Principia," and continue today in debates over the very possibility of such rules. Bringing together key primary sources spanning almost four centuries, "Science Rules" introduces readers to scientific methods that have played a prominent role in the history of scientific practice.

Editor Peter Achinstein includes works by scientists and philosophers of science to offer a new perspective on the nature of scientific reasoning. For each of the methods discussed, he presents the original formulation of the method; selections written by a proponent of the method together with an application to a particular scientific example; and a critical analysis of the method that draws on historical and contemporary sources.

The methods included in this volume are Cartesian rationalism with an application to Descartes' laws of motion; Newton's inductivism and the law of gravity; two versions of hypothetico-deductivism--those of William Whewell and Karl Popper--and the nineteenth-century wave theory of light; Paul Feyerabend's principle of proliferation and Thomas Kuhn's views on scientific values, both of which deny that there are universal rules of method, with an application to Galileo's tower argument. Included also is a famous nineteenth-century debate about scientific reasoning between the hypothetico-deductivist William Whewell and the inductivist John Stuart Mill; and an account of the realism-antirealism dispute about unobservables in science, with a consideration of Perrin's argument for the existence of molecules in the early twentieth century.

While the scientist works essentially with what he observes, with the measurable properties of nature, the philosopher of science is concerned to formulate the conceptual foundations of the scientific method. In this systematic study, Professor Achinstein analyzes such concepts as definitions, theories, and models, and contrasts his view with currently held positions that he finds inadequate.